At present radio communication systems such as mobile phone systems and wireless LANs (Local Area Networks) are widely used. With radio communication a transmission apparatus performs error-correction encoding and modulation on data, maps a modulated signal obtained to a radio resource in a physical layer, and transmits it. A receiving apparatus extracts the signal mapped to the radio resource, performs demodulation and error-correction decoding on the signal, and reproduces the data. With 3GPP (3rd Generation Partnership Project), for example, specifications in the physical layer of a mobile phone system are discussed.
A MIMO (Multiple Input Multiple Output) technique in which a plurality of antennas are used for transmitting and receiving radio signals may be used in a radio communication system. With MIMO the phases of signals transmitted from the plurality of antennas can be adjusted (precoding) according to communication channel fluctuation. For example, a possible method is to select a precoding matrix corresponding to communication channel fluctuation from a set of precoding matrices (code book) in which a phase adjustment amount is defined and to apply it to a signal to be transmitted.
In addition, with a radio communication system a CoMP (Coordinated Multiple Point) transmission technique in which a plurality of transmission apparatus transmit the same data in cooperation with one another is discussed. A receiving apparatus can improve receiving quality by combining received signals each including the same data. CoMP transmission may be performed, for example, in the case where a receiving apparatus measures the receiving power of a signal transmitted from each transmission apparatus and where the difference between the strongest receiving power and the second strongest receiving power is smaller than or equal to a threshold. Furthermore, the CoMP transmission may be performed in the case where the SINR (Signal to Interference and Noise Ratio) of a signal the receiving power of which is strongest is smaller than or equal to a threshold assuming single point transmission.
With the CoMP transmission each transmission apparatus may transmit not only a RS (Reference Signal) specific thereto but also a RS specific to a receiving apparatus in order to make channel estimation of combined signals easy. In addition, the precoding technique may be used in the CoMP transmission.
Moreover, a communication apparatus for performing scheduling of data transmission and a radio transmission apparatus for performing radio processing may be used as two different apparatuses.